The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly includes at least one head, typically several, for reading and writing data from and to the disk. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The head stack assembly includes an actuator assembly, at least one head gimbal assembly, and a flex circuit assembly. A conventional “rotary” or “swing-type” actuator assembly typically includes a rotary actuator having an actuator body. The actuator body has a pivot bearing cartridge to facilitate rotational movement of the actuator assembly. An actuator coil is supported by the actuator body and is configured to interact with one or more magnets, typically a pair, to form a voice coil motor. One or more actuator arms extend from an opposite side of the actuator body.
The spindle motor typically includes a spindle motor base, a spindle motor shaft, a rotatable spindle motor hub, a stator disposed at the disk drive base, a magnet attached to the spindle motor hub, and a bearing cartridge disposed between the spindle motor shaft and the spindle motor hub to facilitate rotational attachment of the spindle motor hub to the spindle motor base. The spindle motor hub may support one or more of the disks that may be separated by disk spacers. A disk clamp may be used to secure the disks to the spindle motor hub. The various rotating elements associated with the disks may be referred to as a disk pack.
The stator typically includes a series of coils that are in electrical communication with the printed circuit board assembly. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby imparting a rotational motion onto the spindle motor hub. Rotation of the spindle motor hub results in the rotation of the overall disk pack including the attached disks.
A topic of concern is rotational balancing of the spindle motor and the overall disk pack. It is important that the mass of the disk pack be balanced so as to reduce dynamic vibrations during operation of the disk drive. Excessive imbalance can degrade the disk drive performance not only in terms of read/write errors, but also in terms of seek times. Excessive imbalance may result in an undesirable acoustic signature and may even result in damage or excessive wear to various disk drive components.
The disk inner surface of each disk is slightly larger in diameter than an outer periphery of the spindle motor hub in order to allow the disks to slip about the spindle motor hub during installation. It is contemplated that the disks may be positioned in an inexact concentric manner about the spindle motor hub. In fact, the disks may be intentionally biased against the spindle motor hub. This results in the disk pack becoming imbalanced in two respects. First, the rotating mass of each biased disk results in a centrifugal force radially extending in a direction from the axis of rotation in a plane orthogonal to the axis of rotation that includes the axis of rotation. This is sometimes referred to as a single plane or “static” imbalance. Second, the same centrifugal force also results in a moment about an axis extending from the axis of rotation in a plane orthogonal to the axis of rotation through the axis of rotation. This is sometimes referred to as a two plane or “dynamic” imbalance.
Accordingly, there is a need in the art for an improved configuration for balancing of the spindle motor and/or the overall disk pack.